1. Technical Field
The present invention relates to a flexural resonator element and a flexural resonator.
2. Related Art
In general, a flexural resonator element includes a vibrating beam. Flexural vibration of the beam causes oscillation to drive the flexural resonator element. When the flexural resonator element is driven, flexural deformation of the beam repeatedly occurs. At a certain moment, when the beam is flexurally deformed, compression displacement is caused in a region near a first side surface of the beam in a deforming direction, and expansion displacement is caused in a region near a second side surface of the beam opposite to the first side surface thereof. Thereby, at the moment, temperature in the compressed region of the beam increases, whereas temperature in the expanded region of the beam decreases. Then, at a next moment, the beam is deformed in a direction opposite to the above deforming direction, whereby the compressed region and the expanded region are switched each other.
When focusing attention on the compressed or expanded region, a cycle of increase and decrease in temperature is repeated in the region by vibration of the beam. Accordingly, when heat input or output occurs between the compressed or expanded region and another region, vibration energy of the beam is dissipated as heat energy, reducing vibration energy efficiency in the flexural resonator element. Such an energy loss is more noticeable in more compact flexural resonator elements and seems to be one of reasons why miniaturization of flexural resonator elements results in a small Q value.
To solve the problem, for example, JP-UM-A-2-032229 discloses a resonator including a hole and a groove. The hole has a same opening area both on upper and lower surfaces of a beam to allow a compressed or expanded region to be structurally independent from an other region. The groove is provided to delay the input or output of heat between the compressed or expanded region and the other region.
Miniaturization of flexural resonator elements has increasingly been demanded. To meet the demand, there is used a beam having an extremely small width. This makes it very difficult to form a groove as in the conventional art on the beam in order to increase the efficiency in the resonator element. In other words, although there is a need for formation of a narrow groove with a large depth, it is more difficult to form a narrower groove by an ordinary etching process. Additionally, mechanical strength of the beam is reduced by formation of the penetrating through-hole having the same opening area both on the upper and the lower surfaces of the beam.
Furthermore, a wiring electrode formed on the beam having a small width needs to also have a small size. This tends to cause wiring electrode breaking or unnecessary short circuit.